The Obama administration made a last-ditch attempt on Thursday to drum up Democratic support to salvage a faltering $1.1 trillion spending bill, just hours ahead of a midnight U.S. government shutdown deadline.

Administration officials from President Barack Obama down to staff at the Department of Education were phoning Democrats in the House of Representatives to ask them to set aside objections to a financial provision and pass the measure to fund most of the government through September.

Obama dispatched his chief of staff, Denis McDonough, to Capitol Hill to speak at a rare evening meeting of House Democrats.

But the outcome hung in the balance even as Obama and House Speaker John Boehner, who have battled each other for the past four years over budget bills, found themselves teaming up to win passage of this one.

"Sweating it," Senate Appropriations Committee Chairwoman Barbara Mikulski said. The Senate Democrat said she did not know whether enough of her fellow House Democrats would rally and lend their support to the legislation she labored over for months.

As Obama and his deputies lobbied Democrats, Boehner launched a similar effort to bring reluctant conservative Republicans on board after delaying a mid-afternoon vote to drum up more support.

Both liberal Democrats and conservative Republicans were still urging their colleagues to oppose it. A provision to roll back part of the Dodd-Frank financial reform law has incensed the left, while those on the right are unhappy that the bill fails to fight Obama's immigration reform.

Congressional aides in both parties insisted that Congress would not allow the government to shut down.

Republicans had prepared backup plans for short-term funding extensions of up to three months in case the bill fails, aides in both parties said.

The 1,603-page measure, negotiated by Republican and Democratic appropriators and leaders, sparked a revolt when rank-and-file Democrats discovered it would kill planned restrictions on derivatives trading by large banks, allowing them to continue trading swaps and futures in units that benefit from federal deposit insurance and Federal Reserve loans.

The Obama administration and Democratic lawmakers also were worried about setting a precedent that emboldens Republicans to cram more Dodd-Frank rollbacks into must-pass legislation, especially when Republicans have control over both chambers of Congress next year.

The Dodd-Frank regulatory overhaul was enacted in the wake of a financial crisis triggered partly by the collapse of complex mortgage derivatives.

While the White House said it objected to the Dodd-Frank provision, its mobilization to secure passage showed it put more value in securing full-year spending for all but one agency. A senior Democratic aide said administration officials were telling party members they should take the spending deal because funding for many of their priorities "is going to get a lot tougher next year" when Republicans control both the House and Senate.

The Pentagon and other agencies also would lose billions of dollars in extra funding in the proposed bill to fight Islamic State militants in Iraq and Syria and Ebola in West Africa if it fails.

Some Democrats also demanded the removal of a provision that allows a massive increase in individual contributions to national political parties for federal elections, potentially up to $777,600 a year.

If it survives, the spending bill would provide the Department of Homeland Security with funds through Feb. 27. The Republicans intend to deny funding to the agency for implementation of Obama's order allowing millions of undocumented immigrants to stay and work in the United States.